The present invention relates to a contact system having a two-armed rotatable contact arm. Contact systems of this kind are used in particular in current-limiting circuit breakers.
German Patent Document No. DE 34 31 288 A1 describes a contact system that has a two-armed contact arm, rotatable about a central bearing arrangement, that is equipped at each of its ends, on opposite sides of a longitudinal axis crossing the rotation axis of the bearing arrangement, with a contact piece that can be brought into and out of contact with a respective contact piece of a stationary busbar, and each of whose lever arms has associated with it a contact force torsion spring that braces against a switching shaft. The bearing arrangement of the contact arm has a bearing pin and, surrounding the bearing pin, an elongated hole whose longitudinal axis extends approximately at right angles to the longitudinal axis of the contact arm. European Patent Document No. EP 869 498 A2 describes a similar contact system having an elongated hole arranged in similar fashion, in which a contact force tension spring is arranged on each side of the contact arm. The tension springs are hooked at both ends into spring pegs that are guided in recesses, extending parallel to the elongated hole, of switching shaft segments, and act upon oppositely located engagement surfaces of the lever arms. European Patent Document No. EP 314 540 B1 describes a contact system having a two-armed contact arm that is floatingly mounted about a virtual rotation axis solely by way of the contact force springs that engage respectively on a lever arm and a switching shaft segment. The known contact systems guarantee equalization even if the contact pieces have an asymmetrically decreasing height, which occurs as a consequence of arc erosion or other wear on said contact pieces, or because of displacement of the rotation axis via the elongated hole or the floating bearing arrangement. It is disadvantageous, however, that in the event of uneven wear on the contact pieces to be associated with the oppositely located ends of the lever arms, when the contact arm is displaced, the contact force springs to be associated with the two lever arms are acted upon differently and/or engage on the lever arms with different distances with respect to the bearing axis, and therefore result in differing contact forces between the connected contact pieces. The consequence of this is moreover that the contact pressure decreases on the side with the most heavily eroded contact pieces, and thus brings about self-reinforcing additional wear on the contact pieces on that side.
It is therefore an object of the present invention to provide a contact system with uniform contact pressure in the event of differing wear on the contact pieces.
The present invention provides a contact system including a contact arm (3), including two lever arms (8; 9) and rotationally symmetrical about 180xc2x0, that is equipped at its opposite ends with contact pieces (10; 11) and is mounted with an elongated hole (5) rotatably on a central bearing axis (7). Stationary busbars (14; 15) are provided having contact pieces (12; 13) that come in contact-closing fashion into contact with, and in contact-opening fashion out of contact with, respective contact pieces (10; 11) of the contact arm (3) located opposite them. Also provided are contact force springs (17; 18) that engage respectively between each of the lever arms (8; 9) and a switching shaft or a switching shaft segment (25). The elongated hole (5) is set, opposite to the opening movement of the contact arm (3), substantially obliquely with respect to its longitudinal axis (29) which runs perpendicular to the initial opening movement of its contact pieces (10; 11) and intersects the bearing axis (7). When the contact system is closed, the action direction (26) between the engaging ends (20, 21; 22, 23) of the contact force springs (17; 18) runs substantially obliquely with respect to the longitudinal axis (29), but not perpendicular or approximately perpendicular to the extension direction (27) of the elongated hole (5).
The present invention provides an oblique incidence of the elongated hole with respect to the longitudinal axis of the contact arm, as well as an oblique alignment of the contact force springs in terms of their longitudinal applied force, i.e., the force line between the engagement points of the corresponding contact force springs on the associated lever arm of the contact arm and on the switching shaft or switching shaft segment, with respect to the longitudinal axis of the contact arm and the profile of the elongated hole. If differing wear occurs on the contact pieces on opposite sides of the contact arm, a forced displacement of the rotation axis of the contact arm thus occurs, inside the obliquely incident elongated hole and about the bearing axis, so as to result, for the contact force springs associated with the two lever arms, in deliberately provided longitudinal action directions and changes in spring length that lead to considerable equalization of the contact forces on both sides of the contact arm.
According to an embodiment of the present invention, the elongated hole is offset by a first angle of 45xc2x0 to 60xc2x0, and the longitudinal action direction of the contact force springs by a second angle of 47xc2x0 to 62xc2x0, with respect to the direction perpendicular to the longitudinal axis of the contact arm.
The contact force springs may be configured as tension springs; they are not limited thereto, however, but can also be used in suitable fashion for the present invention in a different configuration, for example as compression or torsion springs.